Disentangling the impact of local landscape structure & farm management strategies on pollination services by bees: A case study in Costa Rican coffee

by Leslie Spencer

Mentor: Colin Orians, Environmental Studies; funding source: Laura and Martin Bendetson Endowed Summer Scholars Fund

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Biodiversity conservation and agriculture often exist at odds. Costa Rica only occupies 0.03% of the Earth’s land but is estimated to hold 6% of our planet’s biodiversity (Embajada de Costa Rica). However, currently, this globally significant biodiversity is threatened by factors such as climate change and industrial agriculture. Agriculture is an incredibly important part of Costa Rica’s culture and economy, specifically coffee cultivation, so this case system offers an ideal living laboratory to study issues at the nexus of human development and conservation with respect to a certain ecosystem service: pollination.

Costa Rica is well-known for producing high-quality coffee that is sold in specialty markets. A large number of small farmers depend on coffee cultivation for their livelihoods, adding urgency to understanding how to manage coffee farms to be resilient in the face of change. In this study, I focus on understanding the distribution of pollinators (namely, bees) in coffee agroecosystems and the resulting pollination services that they supply to coffee crops. Although coffee is self-fertile, research has shown that pollination by bees significantly increases coffee yields, which provides incentive to farmers to manage their farms to be pollinator-friendly.

There are two landscape elements that are of critical importance to pollinator persistence: nesting sites and floral resources. Both local landscape structure and on-farm management strategies can impact pollinator persistence on farms by altering resource availability. Understanding how to manage coffee farms to have abundant, and arguably more important, diverse pollinator communities is beneficial to create farming systems that won’t collapse in the face of change. In addition to bolstering coffee yields, diverse bee communities help buffer temporal changes in bee species abundance, creating stable, resilient pollinator communities.

Through this literature review, I found that there is no consensus as to how to manage a coffee farm for robust pollinator communities. Typically, we view conservation of natural areas as a beneficial tool to provide ecosystem services to nearby landscapes. However, in the case of pollination services on coffee farms, I found evidence of a biodiversity mismatch. By that I mean that we would typically think that conserving forest fragments near farms would support pollinator communities whose services would spill over onto the farm, however, that spillover effect does not always occur depending on the size of the conserved area. In some cases, if a forest fragment is large enough, it can supply bees with all the resources they need inside the forest, leaving them with little incentive to venture out into nearby coffee crops that only flower during limited windows each year.

These contradictions in the literature have led me to ask further questions: 1) Is there a threshold at which forest fragments near a farm are beneficial vs. detrimental regarding the provisioning of pollination services to coffee crops? 2) What is the value of intact forest surrounding a mono-culture coffee farm compared to a poly-culture coffee farm where shade trees are dispersed throughout the coffee plants? Would pollination services differ between those two farming strategies? 3) How do different conservation strategies impact bee functional diversity? In other words, do certain methods favor some bee functional traits over others (e.g. flight range, nesting sites, body size)?

This year for my senior thesis, I will be diving deeply into these questions using spatial modeling software (such as ArcGIS and InVEST) to better assess and predict pollination services across heterogeneous coffee farm landscapes in Costa Rica. These ecological dynamics are important to understand because coffee in Costa Rica is grown across diversely managed small farms. Some researchers success that the myriad of management practices in use are due to the lack of a holistic understanding of how to farm sustainably and maintain high yields at the same time. Elucidating patterns of pollination dynamics in Costa Rican coffee can provide insight into land-management recommendations that will promote sustainable agriculture in the tropics, a region of great conservation value. Instead of existing at odds, hopefully agriculture and conservation can actually work together in synergy.